define indicator and classification of indicator

indicators are weak organic acids or bases that are used to detect the equivalence point for the titration of an acid by a base .

indicator is a substance that changes the colour at the equivalent point .

the colour change takes place when a certain PH value is reached in the case of acid base indicators.

 depending on the type of titration indicators may be classified into three classes 

1. acid base or neutralization indicators

 are used for acid base titration for example methyl orange indicators 

2.redox indicators

this are used for redox titration for example diphenylamine

 3. adsorption indicators

 this are used for precipitation titration for example rodhomin